Ethambutol is indicated for the treatment of pulmonary tuberculosis. It should not be used alone as a single anti-tubercular drug; instead, it should be used in combination with at least one other anti-tubercular medicine. The choice of the accompanying drug should be based on clinical experience, comparative safety, and appropriate in vitro susceptibility testing.

In patients who have not received previous anti-tubercular treatment (initial treatment), the most commonly used regimens include:

• Ethambutol plus isoniazid
• Ethambutol plus isoniazid plus streptomycin

In patients who have previously received anti-tubercular therapy, resistance to drugs used in initial treatment is common. Therefore, in such retreatment cases, Ethambutol should be combined with at least one second-line anti-tubercular drug that the patient has not previously received and to which the organism has been shown to be susceptible by appropriate in vitro studies. Anti-tubercular medicines used with Ethambutol may include cycloserine, ethionamide, pyrazinamide, viomycin, and other agents. Isoniazid, aminosalicylic acid, and streptomycin have also been used in multidrug regimens. In some cases, alternating drug regimens have also been employed.

Ethambutol appears to act by inhibiting the synthesis of one or more essential metabolites in susceptible bacteria. This disruption impairs cellular metabolism, stops bacterial multiplication, and eventually leads to cell death. Ethambutol is active only against susceptible bacteria that are actively dividing.

Ethambutol should not be used alone, in initial treatment or in retreatment. Ethambutol should be administered on a once every 24-hour basis only. Absorption is not significantly altered by administration with food. Therapy, in general, should be continued until bacteriological conversion has become permanent and maximal clinical improvement has occurred.

Ethambutol is not recommended for use in pediatric patients under thirteen years of age since safe conditions for use have not been established.

Initial Treatment: In patients who have not received previous antituberculous therapy, administer Ethambutol 15 mg/kg of body weight, as a single oral dose once every 24 hours. In the more recent studies, isoniazid has been administered concurrently in a single, daily, oral dose.

Retreatment: In patients who have received previous antituberculous therapy, administer Ethambutol 25 mg/kg of body weight, as a single oral dose once every 24 hours. Concurrently administer at least one other antituberculous drug to which the organisms have been demonstrated to be susceptible by appropriate in vitro tests. Suitable drugs usually consist of those not previously used in the treatment of the patient. After 60 days of Ethambutol administration, decrease the dose to 15 mg/kg of body weight, and administer as a single oral dose once every 24 hours.

During the period when a patient is on a daily dose of 25 mg/kg, monthly eye examinations are advised.

Renal Impairment: Dose adjustment may be needed as determined by blood levels of ethambutol.

The absorption of Ethambutol may be delayed or reduced when it is taken together with aluminium hydroxide.

Ethambutol is contraindicated in patients with known hypersensitivity to this medicine. It is also contraindicated in patients with known optic neuritis, unless in the physician’s judgment the potential benefit justifies its use. In addition, Ethambutol should not be used in patients who are unable to recognize or report visual side effects or changes in vision.

Ethambutol may cause retrobulbar neuritis, which can lead to reduced visual acuity, narrowing of the visual field, central or peripheral scotoma, and red-green color blindness in one or both eyes. It may also reduce the renal clearance of urate, which can trigger acute gout. Other possible adverse effects include confusion, disorientation, hallucinations, headache, dizziness, malaise, jaundice, transient liver dysfunction, peripheral neuropathy, thrombocytopenia, pulmonary infiltrates, eosinophilia, and gastrointestinal disturbances such as nausea, vomiting, loss of appetite, and abdominal pain. In rare cases, retinal hemorrhage, hypersensitivity reactions including rash and itching, leucopenia, fever, and joint pain may occur.

Pregnancy Category C. Animal studies have shown adverse effects on the fetus, or adequate controlled studies in pregnant women are not available. Therefore, Ethambutol should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Ethambutol should be used with caution in patients with ocular disorders, such as cataract, recurrent inflammatory eye conditions, or diabetic neuropathy. Caution is also advised in patients with renal impairment, as well as during pregnancy and lactation.

Anti-tubercular chemotherapeutic agent.

Store at 20°C to 25°C. Protect from light, moisture, and excessive heat.